1. The Field of the Invention
The present invention relates generally to apparatus and methods for improving vascular blood flow, and more particularly to apparatus and methods for improving venous blood flow from peripheral vessels.
2. The Relevant Technology
Blood clotting is a body's natural response at the site of a cut to help seal damaged blood vessels and minimize blood loss. However, a blood clot can also form in an intact vessel, in an inflamed vessel, or in a vessel that contains fatty deposits. Clots tend to form when blood flow is sluggish or in circumstances where there is a rise in the level of coagulation factors in the blood. Deep vein thrombosis, for example, is a condition wherein such clotting occurs within deep-lying veins, especially of the leg. Deep vein thrombosis is common in people with heart failure and in those who have suffered strokes or who are immobilized for long periods of time. In addition, deep vein thrombosis commonly occurs after knee, hip, or abdomen surgery. Age and obesity are also contributory factors. Symptoms of deep vein thrombosis include pain, tenderness, swelling, discoloration, and ulceration of the skin.
Once a clot has formed, it may provide a site for further clotting along the length of the vein. These clots, known as thrombi, can cause pain and damage to the tissues served by the vessel. A clot, or thrombus, that breaks away from the vessel into the blood stream is called an embolus. A "pulmonary embolism" can occur when an embolus travels from peripheral veins through the heart to the lungs via a pulmonary artery. In the lungs, the emboli can be trapped in the ever-decreasing branches of the bronchi. If the embolus is large enough to block the pulmonary artery, or if there are many emboli, the condition can be life threatening. Physicians have long sought effective procedures capable of averting this condition.
One approach used by physicians has involved the administration of anticoagulant drugs such as heparin. Anticoagulant drugs are given in an effort to reduce the clotting ability of the blood and the chance of more clots occurring. However, anticoagulants may be contraindicated in many patients. For example, these drugs may detrimentally result in abnormal bleeding in different parts of the body of the patient and may hinder necessary clotting at a surgical site.
Physicians have also recommended that a patient become ambulatory, or walk around, as soon as possible after surgery. However, it should be appreciated that this is not always feasible for many post-operative patients. In fact, patients who have undergone serious surgical procedures may not be ambulatory for an indeterminate period of time after the surgery.
Physicians have also utilized special elastic stockings, which apply rather tight pressure at the foot and gradually decreasing pressure up to the thigh or pelvis, in an attempt to avert deep vein thrombosis. These stockings are typically opaque and limit the ability of health care personnel to visualize the limb beneath the stocking, except for small fenestrations at the toe area. Thus, in order to monitor the condition of the limb, the stockings must be removed repeatedly throughout use.
In theory, elastic stockings allow a high degree of mobility for the patient. However, in practice, maintaining the stockings at the thigh or pelvis level during ambulation has presented a problem, and garters are often necessitated to hold the stockings in place. It should be appreciated that male patients are generally displeased, if not completely uncooperative, about wearing stockings with garters.
Yet, stockings that roll down present further problems for the patient. Because the stockings increase in pressure as they approach the foot, a tourniquet effect is created when the stockings roll down. Essentially, increased pressures result when the stockings roll down due to doubling or tripling of compressive layers, which generally has the effect of doubling or tripling the applied pressure. Blood flow actually becomes blocked, which may result in ischemic damage to distal tissues and further clotting of the stagnant blood. Thus, elastic stockings actually necessitate close monitoring by health care personnel in order to prevent the tourniquet effect. Surprisingly, elastic stockings are often given to home care patients where little, if any, monitoring is available.
In addition, elastic stockings are not "one size fits all." An imprecise fit can lead to too much pressure and the tourniquet effect if the stockings are too small, and to a substantially diminished effect if the stockings are too large. Therefore, the effectiveness of the elastic stockings typically depends upon a fitting prior to use. Yet, this may be burdensome for the patient, and requires the physician to determine at-risk patients in advance. It should be appreciated that not all procedures associated with the risk for deep vein thrombosis are planned ahead of time. In addition, the fitting requirement necessitates a large inventory of elastic stockings, which may be an inefficient use of capital and stock space.
Another method employed by physicians utilizes pneumatic compression devices. Such devices are generally attached to the patient's calf area while approximately 50 mmHg of pressure is applied for 10-15 seconds and then reduced to atmospheric pressure for 45 to 60 seconds. These devices are also utilized with compression occurring slowly up the calf and thigh in sequential pressure cycles. Pneumatic devices are generally utilized in higher risk patients with reduced mobility because the device itself limits ambulation.
Physicians have also combined the use of elastic stockings and pneumatic devices. However, such a combination presents the problems inherent in the two methods as well as added defects. The cost is virtually doubled, as is the amount of attention required by the medical personnel. Additionally, the devices in concert are hot and uncomfortable. Furthermore, the stocking may roll down beneath the pneumatic device and, as described above, result in a tourniquet effect which increases stagnation and potential clotting of the blood, the very symptoms the devices intended to prevent.